Cements have numerous subterranean applications in oil fields. Primary cementing processes inject cement into the wellbore interstices between the formation face and pipe, such as casing or tubing, as the pipe is being set. The cement bonds the pipe in place to the rock face and also plugs the interstitial voids to prevent fluid communication between different strata immediately behind the wellbore. Squeeze cementing is a secondary process wherein cement is injected into the wellbore interstices to correct prior primary cement jobs, which have failed.
In other applications, cement is injected into a well to shut off very high permeability anomalies existing near the wellbore. These anomalies, such as fractures, fracture networks, thief zones, vugs and are undesirable because they significantly diminish the performance of injection wells by channeling injected flids away from hydrocarbon-rich zones. They also diminish the performance of production wells by promoting premature and extensive water production. Finally, injected cement is used as a permanent plug of abandoned wells.
Portland cement is the most commonly used cement in these applications. U.S. Pat. No. 1,547,189 to Wilson teaches mixing sodium silicate alone with Portland cement in an aqueous medium. The mixture is pumped into an oil well to shut off water entering the wellbore.
A number of other silica containing preparations exist for use in conjunction with well treatment processes. U.S. Pat. No. 2,237,313 to Prutton treats wellbore faces with a liquid silicate mixture to stabilize the rock. The liquid is pumped into the wellbore where it penetrates the rock and hardens over time into a solid gel. U.S. Pat. No. 3,202,214 to McLaughlin teaches the use of sodium silicate gels to shut off permeable zones in a subterranean formation penetrated by a wellbore. U.S. Pat. No. 3,515,216 to Gies describes a process for consolidating sand formations penetrated by a wellbore. The formation is heated to a high temperature by injected steam and then a saturated silica solution is introduced into the formation at a constant flow to effect consolidation. In U.S. Pat. No. 3,965,986 to Christopher, high permeability zones of a subterranean formation are plugged by injecting a liquid colloidal silica suspension and a surfactant into the zones which contact in situ to form a solid gel plug. U.S. Pat. No. 3,990,903 to Mallow teaches a hydrothermal method of cementing a pipe string in a borehole using a cement composition containing a polyvalent metal ion, a hydratable silicate and water. The cement sets upon exposure to high temperature.
The use of silica containing cement is also known in applications unrelated to oil production. U.S. Pat. No. 1,450,467 to Weyland teaches the manufacture of a cement used as a filling for teeth by adding an inorganic base to an aqueous solution of a hydrolyzed organic silicon compound. U.S. Pat. No. 1,587,057 to Winship mixes fused silica with a sodium silicate solution to form a stiff paste. The paste may be molded into any desired form and hardened.
In many cases, cements used in oil field applications perform unsatisfactorily. During curing, Portland cement exhibits excessive shrinkage and filtrate loss and has a protracted set up time. The cured product is brittle and has poor adhesion properties. Silicate cements previously used in oil field applications are inadequate over a broad range of formation conditions. If the cement is incompatible with the formation conditions, it may fail to harden.
An improved cement and cementing process are needed for primary and secondary cementing of wellbores, plugging wellbores or shutting off near-wellbore, very high permeability anomalies. A process is needed whereby a pumpable cementing composition can be injected into a well to perform these functions by setting up over a broad range of subterranean conditions.